2,698 research outputs found
Dyon condensation in topological Mott insulators
We consider quantum phase transitions out of topological Mott insulators in
which the ground state of the fractionalized excitations (fermionic spinons) is
topologically non-trivial. The spinons in topological Mott insulators are
coupled to an emergent compact U(1) gauge field with a so-called "axion" term.
We study the confinement transitions from the topological Mott insulator to
broken symmetry phases, which may occur via the condensation of dyons. Dyons
carry both "electric" and "magnetic" charges, and arise naturally in this
system because the monopoles of the emergent U(1) gauge theory acquires gauge
charge due to the axion term. It is shown that the dyon condensate, in general,
induces simultaneous current and bond orders. To demonstrate this, we study the
confined phase of the topological Mott insulator on the cubic lattice. When the
magnetic transition is driven by dyon condensation, we identify the bond order
as valence bond solid order and the current order as scalar spin chirality
order. Hence, the confined phase of the topological Mott insulator is an exotic
phase where the scalar spin chirality and the valence bond order coexist and
appear via a single transition. We discuss implications of our results for
generic models of topological Mott insulators.Comment: 14 pages, accepted to the New Journal of Physic
Demonstrating the model nature of the high-temperature superconductor HgBaCuO
The compound HgBaCuO (Hg1201) exhibits a simple tetragonal
crystal structure and the highest superconducting transition temperature
(T) among all single Cu-O layer cuprates, with T = 97 K (onset) at
optimal doping. Due to a lack of sizable single crystals, experimental work on
this very attractive system has been significantly limited. Thanks to a recent
breakthrough in crystal growth, such crystals have now become available. Here,
we demonstrate that it is possible to identify suitable heat treatment
conditions to systematically and uniformly tune the hole concentration of
Hg1201 crystals over a wide range, from very underdoped (T = 47 K, hole
concentration p ~ 0.08) to overdoped (T = 64 K, p ~ 0.22). We then present
quantitative magnetic susceptibility and DC charge transport results that
reveal the very high-quality nature of the studied crystals. Using XPS on
cleaved samples, we furthermore demonstrate that it is possible to obtain large
surfaces of good quality. These characterization measurements demonstrate that
Hg1201 should be viewed as a model high-temperature superconductor, and they
provide the foundation for extensive future experimental work.Comment: 15 pages, 6 Figure
Influence of oxygen vacancy on the electronic structure of HfO film
We investigated the unoccupied part of the electronic structure of the
oxygen-deficient hafnium oxide (HfO) using soft x-ray absorption
spectroscopy at O and Hf edges. Band-tail states beneath the
unoccupied Hf 5 band are observed in the O -edge spectra; combined with
ultraviolet photoemission spectrum, this indicates the non-negligible
occupation of Hf 5 state. However, Hf -edge magnetic circular dichroism
spectrum reveals the absence of a long-range ferromagnetic spin order in the
oxide. Thus the small amount of electron gained by the vacancy formation
does not show inter-site correlation, contrary to a recent report [M.
Venkatesan {\it et al.}, Nature {\bf 430}, 630 (2004)].Comment: 5 pages, 4 figures, submitted to Phys. Rev.
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A bed nucleus of stria terminalis microcircuit regulating inflammation-associated modulation of feeding
Loss of appetite or anorexia associated with inflammation impairs quality of life and increases morbidity in many diseases. However, the exact neural mechanism that mediates inflammation-associated anorexia is still poorly understood. Here we identified a population of neurons, marked by the expression of protein kinase C-delta, in the oval region of the bed nucleus of the stria terminalis (BNST), which are activated by various inflammatory signals. Silencing of these neurons attenuates the anorexia caused by these inflammatory signals. Our results demonstrate that these neurons mediate bidirectional control of general feeding behaviors. These neurons inhibit the lateral hypothalamus-projecting neurons in the ventrolateral part of BNST to regulate feeding, receive inputs from the canonical feeding regions of arcuate nucleus and parabrachial nucleus. Our data therefore define a BNST microcircuit that might coordinate canonical feeding centers to regulate food intake, which could offer therapeutic targets for feeding-related diseases such as anorexia and obesity.NARSAD Young Investigator Award from the Brain & Behavior Research Foundation; Bio5 Institute at the University of ArizonaOpen access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Quantum dot-doped porous silicon metal–semiconductor metal photodetector
In this paper, we report on the enhancement of spectral photoresponsivity of porous silicon metal–semiconductor metal (PS-MSM) photodetector embedded with colloidal quantum dots (QDs) inside the pore layer. The detection efficiency of QDs/PS hybrid-MSM photodetector was enhanced by five times larger than that of the undoped PS-MSM photodetector. The bandgap alignment between PS (approximately 1.77 eV) and QDs (approximately 1.91 eV) facilitates the photoinduced electron transfer from QDs to PS whereby enhancing the photoresponsivity. We also showed that the photoresponsitivity of QD/PS hybrid-MSM photodetector depends on the number of layer coatings of QDs and the pore sizes of PS.Published versio
Isotropic three-dimensional gap in the iron-arsenide superconductor LiFeAs from directional heat transport measurements
The thermal conductivity k of the iron-arsenide superconductor LiFeAs (Tc ~
18K) was measured in single crystals at temperatures down to T~50mK and in
magnetic fields up to H=17T, very close to the upper critical field Hc2~18T.
For both directions of the heat current, parallel and perpendicular to the
tetragonal c-axis, a negligible residual linear term k/T is found as T ->0,
revealing that there are no zero-energy quasiparticles in the superconducting
state. The increase in k with magnetic field is the same for both current
directions and it follows closely the dependence expected for an isotropic
superconducting gap. There is no evidence of multi-band character, whereby the
gap would be different on different Fermi-surface sheets. These findings show
that the superconducting gap in LiFeAs is isotropic in 3D, without nodes or
deep minima anywhere on the Fermi surface. Comparison with other iron-pnictide
superconductors suggests that a nodeless isotropic gap is a common feature at
optimal doping (maximal Tc).Comment: 4 pages, 3 figure
Embolic Infarction Associated with Cardiac Amyloidosis
Embolic cerebral infarction due to cardiac amyloidosis is rare. We report two patients with amyloidosis who developed cerebral infarcts. These embolic infarcts were probably related to cardiac involvement of amyloidosis, which was based on results of myocardial biopsy (Patient 1), and kidney biopsy and characteristic echocardiographic features including granular sparkling, restrictive cardiomyopathy and the presence of mural thrombus (Patient 2). Diffuse amyloid infiltration of the heart may have lead to impairment of myocardial function and subsequent mural thrombosis. Cardiomyopathy due to cardiac amyloidosis should be recognized as one of the causes of cardioembolic infarction
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